1. Field of the Invention
This invention relates generally to the field of semiconductor device manufacturing and, more particularly, to a method and apparatus for determining wafer identity and orientation using circumscribed wafer identification marks with unique sector descriptors.
2. Description of the Related Art
During the manufacture of semiconductor devices, semiconductor wafers, each including a plurality of individual die, are subjected to a number of processing steps. Typically, wafers are grouped into lots that are processed together. Each lot may contain, for example, 25 individual wafers. As a lot of wafers progresses through the processing line, the wafers are typically housed in a carrier.
FIG. 1 illustrates a typical semiconductor wafer 10. The wafer 10 includes an orientation notch 20 useful as a reference point for orienting the wafer 10. Some of the processes performed on the wafer 10 (e.g., photolithography) are highly sensitive to wafer orientation. Typically, prior to performing an orientation-sensitive process the wafer is rotated until the notch 20 is located and placed in a predetermined position. For identification purposes, a unique wafer identification code 30 is scribed on the wafer 10 beneath the notch 20 using a laser scribing process where small dots are burned into the surface to construct the characters or symbols of the code. Exemplary wafer identification codes 30 may include alphanumeric identifiers or bar code identifiers (e.g., 1 or 2 dimensional codes). During the production process, process history and metrology information is stored in a database for each of the wafers 10 indexed by its respective wafer identification code 30.
When a lot of wafers 10 is housed in a carrier, only a portion of the periphery of each wafer 10 is visible. If the visible portion includes the notch 20, an optical wafer sorter may read the wafer identification code 30 to discern the identities of the wafer 10. However, if the visible portion does not include the notch 20, the wafer 10 must first be rotated before its identity can be determined. Rotating the wafer 10 sometimes requires that it first be removed from the carrier. The necessity to orient the wafers 10 prior to determining their identities reduces the efficiency of the identification process, and thus, the efficiency of the processing line. Wafer handling also increases the likelihood of damage (e.g., droppage, scratching, cracking, etc.), particulate contamination, and loss or traceability.
Another problem associated with the wafer identification code 30 is that it tends to become harder to read as the wafer 10 progresses through the manufacturing process. Wafers 10 are subjected to a wide variety of processes, such as chemical and physical etching, polishing, annealing, that have a tendency to degrade the wafer identification code 30. In some cases the degradation in the wafer identification code 30 is sufficiently severe that it can no longer be read by the wafer sorter. One technique for countering the degradation is the use of self correcting coding techniques, such as two dimensional bar coding, that encode redundant information in horizontal and vertical patterns. If a portion of the pattern is obscured, the missing information may sometimes be recreated from the redundant information. Even with such information redundancy, some wafer identification codes 30 may still degrade to the point where they are unreadable.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.
One aspect of the present invention is seen in a system for identifying wafers contained in a wafer carrier. Each wafer includes a surface terminating in an edge and a plurality of sector identification codes disposed on the surface proximate the edge. A wafer sorter is adapted to scan at least a portion of a wafer extending from the carrier and to identify at least one of the sector identification codes on the wafer independent of the orientation of the wafer in the wafer carrier.
Another aspect of the present invention is seen in a method for identifying wafers contained in a wafer carrier. Each wafer includes a surface terminating in an edge and a plurality of sector identification codes disposed on the surface proximate the edge. The method includes scanning at least a portion of a wafer extending from the carrier and identifying at least one of the sector identification codes on the wafer independent of the orientation of the wafer in the wafer carrier.